1. Field of the Invention
The present invention relates generally to noise reduction circuits, and more particularly to a method and apparatus for reducing noise in an audio signal.
2. Prior Art
Reducing noise and/or extending dynamic range is very common. The standard way of reducing noise or extending dynamic range for an analog audio signal for wireless transmission is by using a compander (compression and expansion) circuit. Conventional companding amplifiers typically employ circuitry that compresses an audio input signal using a full wave rectifier and peak detector. Then an expanding amplifier uses the peak amplitude for the amount of expansion.
A compander will always affect the analog signal in a negative fashion by causing some compression and noise floor modulation due to the lag time of the expansion circuit. These negative aspects are unacceptable in the pro audio market when high fidelity is required. The alternative is to use digital converters and obtain the required signal integrity. Digital converters have limited dynamic range depending on the amount of power used and technology available and therefore, low power analog to digital converters cannot usually accommodate both the very small and very large signals required in a pro audio environment. 16-20 bits is standard accuracy of existing converters and at 6 dB of dynamic range per bit of accuracy 96 dB-120 dB is the current attainable range. An analog to digital converter with 120 dB of dynamic range uses 3-4 times the power of one with 96 dB of dynamic range. Wireless audio applications require a large dynamic range and usually require battery operation making a suitable converter usable.
The present invention satisfies the need of the pro audio environment by overcoming the audio deficiencies of companders and the power deficiencies of analog to digital and digital to analog converters